Fair Value Option - Components of Gain on Instruments at Fair Value and Related Derivatives (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	$ 324	[1]	$ (49)	[1]	$ 71	[1]	$ (394)	[1]
Credit risk component	107		77		119		(79)
Total mark-to-market on financial instruments designated at fair value	431		28		190		(473)
Net realized loss on the financial instruments	0		0		(8)		(1)
Mark-to-market on the related derivatives	(332)		98		(126)		372
Net realized gain on the related long-term debt derivatives	16		15		32		31
Gain (loss) on instruments designated at fair value and related derivatives	115		141		88		(71)
Loans [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	0	[1]	0	[1]	0	[1]	1	[1]
Credit risk component	0		2		21		34
Total mark-to-market on financial instruments designated at fair value	0		2		21		35
Net realized loss on the financial instruments	0		0		(8)		(1)
Mark-to-market on the related derivatives	0		0		0		0
Net realized gain on the related long-term debt derivatives	0		0		0		0
Gain (loss) on instruments designated at fair value and related derivatives	0		2		13		34
Long-term Debt [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	120	[1]	(123)	[1]	183	[1]	(40)	[1]
Credit risk component	53		131		11		(90)
Total mark-to-market on financial instruments designated at fair value	173		8		194		(130)
Net realized loss on the financial instruments	0		0		0		0
Mark-to-market on the related derivatives	(128)		142		(190)		27
Net realized gain on the related long-term debt derivatives	16		15		32		31
Gain (loss) on instruments designated at fair value and related derivatives	61		165		36		(72)
Hybrid Instruments [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	204	[1]	74	[1]	(112)	[1]	(355)	[1]
Credit risk component	54		(56)		87		(23)
Total mark-to-market on financial instruments designated at fair value	258		18		(25)		(378)
Net realized loss on the financial instruments	0		0		0		0
Mark-to-market on the related derivatives	(204)		(44)		64		345
Net realized gain on the related long-term debt derivatives	0		0		0		0
Gain (loss) on instruments designated at fair value and related derivatives	$ 54		$ (26)		$ 39		$ (33)

[1] As it relates to hybrid instruments, interest rate and other components includes interest rate, foreign exchange and equity contract risks.